7.5
Write-through cache provides safety (the cache always matches memory) at the expense of performance.
a. Use write-back cache to increase performance.
b. Use write-through cache to provide data integrity.
7.9
References in order: miss, miss, miss, miss, miss, miss, miss, miss, miss,
hit, miss, miss, miss, miss, hit
The cache at the end of these references
showing byte addresses (hex) and word addresses (decimal)
| Memory[n]- Memory[n+3] |
|---|
| C0-C4 (word address 48) |
| 8-B (word address 2) |
| C-F (word address 3) |
| 10-13 (word address 4) |
| 54-57 (word address 21) |
| 18-1B (word address 6) |
| 6C-6F (word address 27) |
| 2C-2F (word address 11) |
| 34-37 (word address 13) |
One example of index computation (address reference = 21)
Word Address reference = 0010101
Full Address reference = 0010101XX
index = 0101
tag = 1
Memory locations 54-57 will be loaded into the cache.
7.10
References in order:
miss, hit, miss, miss, miss, miss, miss, miss,
miss, hit, miss, hit, miss, miss, hit, miss
The cache at the end of these references
showing byte addresses (hex) and word addresses (decimal)
| Memory[n]- Memory[n+15] |
|---|
| 0-F (word addresses 0-3) |
| 10-1F (word addresses 4-7) |
| 20-2F (word addresses 8-11) |
| 30-3F (word addresses 12-15) |
One example of index computation (address reference = 11)
Word Address reference = 0001011
Full Address reference = 0001011XX
index = 10
tag = 0
Memory locations 20-2F will be loaded into the cache.
7.28
Consider a cache that contains 4 words so there are 2 sets
in the set-associative cache.
Consider a series of accesses (word addresses in hex) 0, 2, 4
The direct mapped cache will have fewer misses because all three
words map to set - in the set-associative cache.
7.39
Page size = log2(16K) = 14 bits
Virtual page number requires 40 - 14 = 26 bits
Page number requires 36 - 14 = 22 bits
Page table requires 2 26 page table entries
Each page table entry requires 4 + 22 = 26 bits (round up to 32 bits)
Each page table requires 2 26 x 4 bytes/entry = 256 Megabytes
Address Space Problem
Virtual memory was originally created to allow access to a large
physical address space.
e.g. The Eclipse had a 16 bit address space but you could configure
16 MBytes of Ram (if you had the $$$$)