C. Computer Environments and Systems · Computer Environments and Systems

Reading Computer Specifications: Processors, Buses, Memory and Storage

C1.2About 70 minutes

Learning goals

I can explain what processor type, cores, clock speed, bus speed, amount of memory and storage capacity mean, using correct terminology and units.
I can convert between bits, bytes, KB, MB, GB and TB, and explain why a 1 TB drive shows up as about 931 GB.
I can calculate data transfer times and memory bandwidth from specifications.
I can use specifications to decide whether a computer meets a user's needs.

Words to know

bit
A binary digit, 0 or 1: the smallest unit of data.

byte (B)
8 bits. Storage and memory sizes are measured in bytes.

kilobyte, megabyte, gigabyte, terabyte
KB, MB, GB, TB. In the SI (decimal) system each is 1000 times the one before.

KiB, MiB, GiB
Binary units: 1 KiB = 1024 bytes, 1 MiB = 1024 KiB, 1 GiB = 1024 MiB.

processor type (architecture)
The family of instruction sets a CPU understands, such as x86-64 (most Windows PCs) or ARM (phones, tablets, many Chromebooks and recent Macs).

clock speed
How many cycles per second the CPU's clock runs, in gigahertz (GHz). 1 GHz = 1 billion cycles per second.

bus
A set of electrical pathways that carries data between components, such as the CPU and RAM.

bus speed / bandwidth
How fast a bus moves data. Bandwidth = width (bytes per transfer) × transfers per second, measured in MB/s or GB/s.

Mbps vs MB/s
Megabits per second (network and USB speeds) versus megabytes per second. Divide megabits by 8 to get megabytes.

Decoding the spec sheet

Here is a real-looking listing from a back-to-school flyer:

"14-inch laptop. 8-core processor, up to 4.4 GHz, 12 MB cache. 16 GB DDR5-5600 RAM. 512 GB NVMe SSD. Wi-Fi 6. USB-C 10 Gbps."

By the end of this lesson you will be able to explain every part of that sentence, do the arithmetic behind it, and say who it is good for. The last lesson named the components; this lesson is about their numbers.

Units first: bits and bytes

Everything in a computer is stored as bits (0s and 1s). In the Programming Basics unit you see how numbers and text become binary. Here we care about how many bits.

8 bits = 1 byte (B). One byte can hold one plain English letter.
Storage and memory sizes are given in bytes: KB, MB, GB, TB.
Network and USB speeds are usually given in bits per second (Mbps, Gbps). A small b means bits; a capital B means bytes. To turn bits into bytes, divide by 8.

There is one famous trap. Drive makers use decimal prefixes: 1 GB = 1 000 000 000 bytes. Many operating systems (Windows, for example) count in binary units of 1024³ bytes but still write "GB". So a drive sold as 1 TB = 1 000 000 000 000 bytes appears as about 931 GB. Nothing is missing; the two numbers just use different units. To be exact, binary units have their own names: KiB, MiB, GiB (kibibyte, mebibyte, gibibyte). RAM sizes are traditionally binary: a "16 GB" RAM kit holds 16 GiB.

Each storage unit is 1000 times the one before (decimal). Only the first step is different: 8 bits make a byte. Binary units (KiB, MiB, GiB) use 1024 instead of 1000, which is why the same drive can show two different sizes.

drive_bytes = 1_000_000_000_000 # a drive sold as "1 TB"

gib = drive_bytes / 2**30 # 2**30 = 1024 * 1024 * 1024

print("Advertised: 1 TB")

print("Shown by the operating system:", round(gib, 1), "GiB")

This program explains the "missing" space. In Python, two asterisks mean "to the power of", so the second line divides by 2 to the power of 30. Output (one line each): Advertised: 1 TB / Shown by the operating system: 931.3 GiB

Processor type, cores and clock speed

Processor type (architecture). CPUs understand different instruction sets. Most Windows desktops and laptops use x86-64 processors (made by Intel and AMD). Phones, tablets, many Chromebooks and recent Macs use ARM processors, which are known for using less power. Programs must be built for the processor type, which you will see in the lesson Source Code and Machine Code. Within a family, newer generations usually do more work per clock cycle.
Cores. Each core is a complete processing unit. A 6-core CPU can work on 6 streams of instructions at once. Many CPUs also run 2 threads per core, so a "6-core, 12-thread" CPU can keep 12 streams going. More cores help when you run many programs or do work that splits into pieces (video exports, compiling big programs).
Clock speed. Measured in gigahertz. 3.6 GHz means the clock ticks 3.6 billion times per second, and the CPU does a step of work on each tick. Listings often give a base speed and a higher boost ("up to") speed that the CPU reaches for short bursts when it is cool enough.
Cache. Bigger caches (in MB) mean the CPU waits for RAM less often.

Be careful comparing clock speeds. A newer CPU at 3.0 GHz can beat an older one at 3.5 GHz, because it does more work each cycle. Compare CPUs of the same generation, or look at benchmark tests.

Buses and bus speed

A bus is a set of electrical pathways that carries data between components. The memory bus connects the CPU to RAM; PCI Express (PCIe) connects the video card and fast SSDs; USB connects outside devices.

Two numbers decide how fast a bus is:

its width: how many bits travel side by side (a standard RAM channel is 64 bits = 8 bytes wide), and
its speed: how many transfers happen each second.

Bandwidth = bytes per transfer × transfers per second.

RAM labelled DDR4-3200 makes 3200 million transfers per second (MT/s). Each transfer moves 8 bytes, so one stick can move 3200 × 8 = 25 600 MB/s, which is 25.6 GB/s. Many computers use two RAM sticks in dual channel, which doubles this.

A bus is like a highway. Its width is the number of lanes (64 bits side by side) and its speed is how often cars leave (3200 million transfers per second). Together they give the bandwidth.

def bandwidth_gb_s(mt_per_s, width_bits):

bytes_per_transfer = width_bits / 8

return mt_per_s * 1_000_000 * bytes_per_transfer / 1_000_000_000

print("DDR4-3200:", bandwidth_gb_s(3200, 64), "GB/s")

print("DDR5-5600:", bandwidth_gb_s(5600, 64), "GB/s")

A function that turns a RAM label into bandwidth for one 64-bit channel. Output (one line each): DDR4-3200: 25.6 GB/s / DDR5-5600: 44.8 GB/s

Memory and storage: how much is enough?

Amount of memory (RAM). The operating system, browser tabs, an IDE and any game or editor all need RAM at the same time. A common rule of thumb in 2026: 8 GB for basic use (web, documents, video calls), 16 GB for comfortable everyday use and programming, 32 GB or more for heavy video editing, 3-D work or large virtual machines. Always check the recommended requirements printed by the software the user needs.
Storage capacity. Add up what the user needs to keep: the operating system and programs, plus their files, plus room to grow. Leave free space; drives work poorly when nearly full.
Storage speed. Typical speeds for reading large files: a hard drive about 100 to 250 MB/s; a SATA SSD up to about 550 MB/s; an NVMe SSD on PCIe from about 2000 MB/s to more than 10 000 MB/s for the newest PCIe 5.0 drives. Faster storage means faster start-up and quicker loading of programs and big files.

Spec in the listing	What it means	Unit
8-core processor	8 independent processing units	cores
up to 4.4 GHz	boost clock speed: 4.4 billion cycles per second	GHz
12 MB cache	fast memory inside the CPU	MB
16 GB DDR5-5600 RAM	16 GB of working memory; 5600 MT/s ≈ 44.8 GB/s per channel	GB, MT/s
512 GB NVMe SSD	512 GB of fast flash storage on the PCIe bus	GB
USB-C 10 Gbps	port that can move up to 10 gigabits (1.25 gigabytes) per second	Gbps

The flyer from the start of the lesson, decoded.

Worked example

Example 1: How long will the copy take?

Noah copies a 6 GB video (6 000 000 000 bytes) to a USB flash drive. Find the shortest possible time over (a) USB 2.0 at 480 Mbps and (b) USB 3.0 at 5 Gbps.

Speeds are in bits per second, so convert to bytes: (a) 480 000 000 ÷ 8 = 60 000 000 B/s = 60 MB/s. (b) 5 000 000 000 ÷ 8 = 625 000 000 B/s = 625 MB/s.
Time = size ÷ speed. (a) 6 000 000 000 ÷ 60 000 000 = 100 s. (b) 6 000 000 000 ÷ 625 000 000 = 9.6 s.
These are theoretical best cases. Real copies are slower, often because the flash drive itself cannot write that fast. The slowest part of the path decides the speed.

At best about 100 s on USB 2.0 and 9.6 s on USB 3.0: more than 10 times faster, if the flash drive can keep up.

Worked example

Example 2: How much storage does Priya need?

Priya is a photographer. She has 12 000 photos at about 4 MB each and 150 video clips at about 600 MB each. The operating system and programs need about 80 GB. What size SSD should she buy?

Photos: 12 000 × 4 MB = 48 000 MB = 48 GB.
Videos: 150 × 600 MB = 90 000 MB = 90 GB.
Total now: 48 + 90 + 80 = 218 GB.
A 256 GB drive would already be about 85% full (218 ÷ 256 ≈ 0.85), and she will keep taking photos. Choose at least 512 GB, or 1 TB if her library grows quickly; an external drive can also hold older photos (see the lesson on backups).

She needs about 218 GB today, so a 512 GB or 1 TB drive leaves room to grow.

photos_gb = 12000 * 4 / 1000

videos_gb = 150 * 600 / 1000

system_gb = 80

total = photos_gb + videos_gb + system_gb

print("Total needed:", total, "GB")

for size in [256, 512, 1000]:

print(size, "GB drive would be", round(total / size * 100), "% full")

Example 2 as a Python program. Changing the numbers at the top lets you size a drive for any user. Output (one line each): Total needed: 218.0 GB / 256 GB drive would be 85 % full / 512 GB drive would be 43 % full / 1000 GB drive would be 22 % full

Just for fun

Hard-drive makers count in thousands and many operating systems count in 1024s, so a brand-new 1 TB drive seems to "shrink" to 931 GB the moment you plug it in. No bytes were harmed in the making of this unit conversion.

Hands-on activity

Be a spec detective

You need: a computer with Python (or a free browser-based Python such as the one at python.org/shell), and two computer listings from a flyer or a store website.

Copy each listing's specs into a table: processor (cores, clock speed, cache), RAM (amount and type), storage (type and capacity), ports.
For each spec, write what it means in plain words and its unit.
Run the bandwidth program above with each computer's RAM label (for example DDR4-2666 or DDR5-4800). If a listing does not give the RAM speed, write "not given": a good shopper notices missing specs.
Use the storage program to check whether each computer's drive would hold Priya's files with at least 30% free.
Write a short recommendation: which computer is better for a student who programs and edits short videos, and why?

What to look for: correct units (GHz, GB, MT/s, Gbps), correct arithmetic (DDR4-2666 gives 21.3 GB/s per channel; DDR5-4800 gives 38.4 GB/s), and a recommendation that refers to specific specs.

Your turn

How many bits are in 4 bytes?

A drive is sold as 500 GB. About how many GiB will the operating system show? (1 GiB = 1 073 741 824 bytes.)

What does "3.6 GHz" tell you about a CPU?

Your home internet downloads at 100 Mbps. What is the fastest a 1.2 GB file could download?

Find the bandwidth of one channel of DDR4-2666 RAM (64 bits wide).

Why might a 3.0 GHz CPU be faster than a 3.5 GHz CPU?

What is the difference between Mbps and MB/s?

More practice: warm-up

How many bytes are in 3 KB (decimal)?

How many GB are in 2.5 TB (decimal)?

Name the two most common processor types (architectures) found in computers and phones.

What does a bus do?

Which is usually faster at reading files: an NVMe SSD or a hard drive?

More practice: on your own

A phone has 128 GB of storage. The system uses 18 GB, apps use 40 GB, and each minute of 4K video uses about 400 MB. How many full minutes of video can it record?

A game update is 3 GB. How long will it take, at best, on a 50 Mbps connection?

A listing says "16 GB RAM, 1 TB HDD". Another says "16 GB RAM, 512 GB SSD". For a student who wants fast start-up and quick program loading, which is better? Explain.

Explain why the bandwidth of a bus depends on both its width and its speed.

Write one line of Python that prints how many megabits are in 25 megabytes.

Challenge

Two DDR5-4800 sticks run in dual channel (two 64-bit channels working together). What is the total bandwidth?

A clock cycle at 4 GHz takes how long? Give your answer in nanoseconds (1 ns = 0.000 000 001 s).

A store says a laptop has "24 GB memory" made of 8 GB of RAM plus a 16 GB "memory accelerator" on the SSD. Is it fair to call this 24 GB of memory? Explain using the memory hierarchy.

Check your understanding

Quiz

How many bits are in one byte?

A drive sold as 1 TB shows up as about 931 GB on a computer. Why?

What is the bandwidth of one 64-bit channel of DDR4-3200 RAM?

A network speed is given as 80 Mbps. What is that in megabytes per second?

Which statement about CPU clock speed is correct?

Which processor type is used in most phones and tablets?

For parents and teachers

Big idea: Expectation C1.2 asks students to relate computer specifications (processor type, bus speed, storage capacity, amount of memory) to user requirements, using correct terminology. Much of this lesson is unit arithmetic.

How to help: Pick up a store flyer or open a retailer's website together and ask your teen to explain each spec and its unit. Ask "Is that bits or bytes?" whenever a speed appears. Check your home internet plan's speed (in Mbps) and have your teen work out how long a large game or software update should take.

Common difficulties:

Mixing up b (bits) and B (bytes). Speeds are usually in bits; sizes are in bytes.
Expecting 1 TB to show as 1000 GB. Decimal versus binary units explain the difference.
Comparing clock speeds across different CPU generations or makers. Compare like with like, or use benchmarks.
Forgetting that theoretical speeds are maximums; real transfers are slower and limited by the slowest part.