← IGCSE Computer Science Paper 1

NAND and NOR flash

The two ways of arranging flash transistors, named after logic gates. NAND gives high capacity (SSDs, SD cards); NOR gives faster random reads (stored program code).

Part of: IGCSE Computer Science 0478 — 3.3 Data Storage — Module 16

Understanding NAND and NOR flash in IGCSE Computer Science Paper 1

What it does: NAND is the arrangement chosen when large amounts of data must be stored, as in SSDs, SD cards and USB drives. NOR flash lets the processor read any single location quickly, so it suits stored program code such as firmware. The names come from the NAND and NOR logic gates, because the transistors are wired in a similar way. Both types store bits by trapping charge in floating-gate transistors. They differ in how the transistors are arranged. NAND arrangements pack more transistors into a small space, so they hold more data. USB drives need lots of cheap capacity, so they use NAND flash.

Common mistakes: NAND flash is arranged to give high capacity, which is why it is used in SSDs. The value should be "high". NOR flash has faster random reads, so it is used to store program code, not bulk files like video. It should be "program code".

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Learning

Duo

Which type of flash memory is used in SSDs, SD cards and USB drives?

NOR flashNAND flash

Matches

An SSD uses NOR flash because NOR gives the highest capacity

↓

SSDs, SD cards and USB drives use NAND flash, not NOR. It is NAND that gives high capacity.

Applying

Meanings

Term

NAND and NOR flash

Meaning

The two ways of arranging flash transistors, named after logic gates. NAND gives high capacity (SSDs, SD cards); NOR gives faster random reads (stored program code).

Practice

IF use = "SSD" OR use = "SD card" THEN

Testing

Gaps

flash gives high capacity storage

Check Answer

Spots

1nand_capacity = "low"

2nand_use = "SSD"

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Quick Questions

1. Which type of flash memory is used in SSDs, SD cards and USB drives?

A. NAND flash ✓

B. NOR flash

NAND flash gives high capacity at a low cost per gigabyte, so it is used for bulk storage such as SSDs, SD cards and USB drives.

2. Which type of flash memory is better for fast random reads of stored program code?

A. NOR flash ✓

B. NAND flash

NOR flash lets the processor read any single location quickly, so it suits stored program code such as firmware.

3. NAND and NOR are named after...

A. The logic gate each transistor arrangement resembles ✓

B. The company that invented each type

The names come from the NAND and NOR logic gates, because the transistors are wired in a similar way.

4. Which statement about NAND and NOR flash is true?

A. Only NAND uses floating-gate transistors

B. Both use floating-gate transistors to store data ✓

Both types store bits by trapping charge in floating-gate transistors. They differ in how the transistors are arranged.

5. Which flash type gives the higher storage capacity?

A. NOR flash

B. NAND flash ✓

NAND arrangements pack more transistors into a small space, so they hold more data.

Match the Pairs

NAND flash → Flash memory with transistors arranged for high capacity, used in SSDs, SD cards and USB drives

NOR flash → Flash memory with transistors arranged for faster random reads, used to store program code

Flash memory arranged for high capacity is used in storage devices such as SSDs, SD cards and USB drives → NAND flash

Flash memory arranged for fast random reads is used for stored program code → NOR flash

An SSD uses NOR flash because NOR gives the highest capacity → SSDs, SD cards and USB drives use NAND flash, not NOR. It is NAND that gives high capacity.

NAND flash uses floating-gate transistors but NOR flash does not → Both NAND and NOR flash use floating-gate transistors. They differ only in how the transistors are arranged.

Key Term

NAND and NOR flash

The two ways of arranging flash transistors, named after logic gates. NAND gives high capacity (SSDs, SD cards); NOR gives faster random reads (stored program code).

Fill in the Blanks

1. NAND flash gives high capacity storage

Hint: Type the flash type used in SSDs, SD cards and USB drives.

2. NOR flash gives faster random reads

Hint: Type the word for reading from any location directly, not in sequence.

3. Both use floating-gate transistors

Hint: Type the word describing the gate that traps charge to store a bit.

4. NOR flash stores program code

Hint: Type what a program is made of, the instructions NOR flash holds.

5. NAND and NOR are named after logic gates

Hint: Type the plural word for the electronic components these arrangements are named after.

Spot the Error

Question 1

A nand_capacity = "low"

B nand_use = "SSD"

C print(nand_capacity, nand_use)

Line A — NAND flash is arranged to give high capacity, which is why it is used in SSDs. The value should be "high".

Question 2

A nor_read = "fast"

B nor_use = "video files"

C print(nor_read, nor_use)

Line B — NOR flash has faster random reads, so it is used to store program code, not bulk files like video. It should be "program code".

Question 3

A devices = ["SSD", "SD card"]

B for d in devices:

C print(d, "uses NAND")

D print("Code chip uses NAND")

Line D — A chip holding stored program code uses NOR flash for its faster random reads. NAND is used for the SSD and SD card storage.

Question 4

A def flash_type(job):

B if job == "storage":

C return "NOR"

D return "NOR"

Line C — Bulk storage needs high capacity, which is what NAND flash provides. This line should return "NAND"; NOR is the other branch.

Question 5

A nand_gate = "floating"

B nor_gate = "floating"

C print(nand_gate != nor_gate)

Line C — Both NAND and NOR flash use floating-gate transistors, so the comparison should use == and print True.

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