In write-through, a write to a cached location is performed on:

Both cache and main memory together

Main memory when the block is replaced

What does the dirty bit in write-back caching indicate?

The block has been modified in cache but not yet written to memory

The block was loaded by write-allocate

Which statement correctly compares the two techniques?

Write-through is simple but slow with high bus traffic; write-back is faster but may leave memory stale

Write-through has less bus traffic than write-back

Write-back is simpler but keeps memory always current

Both leave memory stale until replacement

2069 Bhadra · 2 marks

Cache write techniques

Short answer

The two main cache write techniques are write-through and write-back. Write-through updates both cache and main memory on every write, keeping memory current but slow. Write-back updates only the cache and sets a dirty bit; the block is written to memory only when evicted, reducing bus traffic but adding complexity.

Describe the cache write techniques.

When the processor writes to a cached location, the cache and main memory must stay consistent. The two techniques are:

Write-through: every write updates both the cache and main memory at once. Memory is always current and the design is simple, but writes are slow (memory-speed) and bus traffic is high.
Write-back (copy-back): a write updates only the cache and sets a dirty bit. The block is written to main memory only when it is replaced. This is faster and gives less bus traffic, but memory may be stale and the hardware is more complex.

A write miss is handled by write-allocate (load the block, then write) or no-write-allocate (write straight to memory).

✓ Answer checked by Claude Opus 5.5 (high effort)

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