Memory Designs: Cache Example Minggu 10

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Memory Designs Cache Example (Minggu 10)
IKI 30210 Organisasi Sistim Komputer Fakultas
Ilmu KomputerUniversitas Indonesia
Johny Moningka (moningka_at_cs.ui.ac.id),
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Administra-trivia

• Tugas kelompok Survei Teknologi Memori.
• Topik
• konsep dasar jenis-jenis semikonduktor memori yg
  penting, istilah dan leading technology.
• Issue penting pilihan teknologi cost, kinerja,
  aplikasi
• Perkembangan teknologi memori (prediksi)
• Buat kelompok (max. 3 orang).
• Referensi
• Computer Org. , Harmacher 3th Edition
• Site internet tomshardware, pcguide, anandtech.
• Ralat batas akhir pengumpulan tugas 7 Des. 2004
  (waktu kelas).

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Memory System

• Teknologi dan Sistem Memori
• Review teknologi memori
• Rancangan Memory Hierarchy
• Cache Memory
• Review Example Cache Operations
• Definition cache miss, hit, miss penalty
• Main Memory Virtual Memory

4
Caching Terminology

• Saat prosesor mengakses memory maka terdapat 3
  kemungkinan
• cache hit blok cache valid dan sesuai dengan
  alamat, word dapat dibaca dari cache
• cache miss tidak ada blok dalam cache, jadi
  mengambil (copy) blok dari memory ke cache
• cache miss, block replacement blok pada cache
  salah (address), ganti blok tersebut dengan
  mengambil blok data dari memory

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Accessing data in a direct mapped cache
Memory

• Ex. 16KB of data, direct-mapped, 4 word blocks
  (16 bytes per block)
• Read 4 addresses
• 0x00000014
• 0x0000001C
• 0x00000034
• 0x00008014
• Memory values on right
• only cache/ memory level of hierarchy

Value of Word
Address (hex)
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Review Memorized this table yet?

• Blah blah Cache size 16KB blah blah 2? blocks
  blah blah how many bits?
• Answer! 2XY means
• X0 ? no suffix
• X1 ? kibi Kilo 103
• X2 ? mebi Mega 106
• X3 ? gibi Giga 109
• X4 ? tebi Tera 1012
• X5 ? pebi Peta 1015
• X6 ? exbi Exa 1018
• X7 ? zebi Zetta 1021
• X8 ? yobi Yotta 1024

Y0 ? 1 Y1 ? 2 Y2 ? 4 Y3 ? 8 Y4 ? 16 Y5 ?
32 Y6 ? 64 Y7 ? 128 Y8 ? 256 Y9 ? 512

WWW gt 170 Tb of information on its surface
Email gt 400 PB of new information/year
worldwide.(www.sims.berkeley.edu/research/project
s/how-much-info-2003/)
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Accessing data in a direct mapped cache

• Contoh mengakses 4 Alamat
• 0x00000014, 0x0000001C, 0x00000034, 0x00008014
• Contoh 4 alamat dibagi atas Tag, Index, Byte
  Offset fields

000000000000000000 0000000001 0100 000000000000000
000 0000000001 1100 000000000000000000 0000000011
0100 000000000000000010 0000000001 0100 Tag
Index Offset
8
16 KB Direct Mapped Cache, 16B blocks

• Valid bit flag bit menentukan apakah isi blok
  dari cache valid (when computer initially turned
  on, all entries invalid)

Index
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1. Read 0x00000014

• 000000000000000000 0000000001 0100

Tag field
Index field
Offset
Index
10
So we read block 1 (0000000001)

• 000000000000000000 0000000001 0100

Tag field
Index field
Offset
Index
11
No valid data

• 000000000000000000 0000000001 0100

Tag field
Index field
Offset
Index
12
So load that data into cache, setting tag, valid

• 000000000000000000 0000000001 0100

Tag field
Index field
Offset
Index
0
1
0
a
b
c
d
0
0
0
0
0
0
0
0
13
Read from cache at offset, return word b

• 000000000000000000 0000000001 0100

Tag field
Index field
Offset
Index
0
1
0
a
b
c
d
0
0
0
0
0
0
0
0
14
2. Read 0x0000001C 000 0..001 1100

• 000000000000000000 0000000001 1100

Tag field
Index field
Offset
Index
0
1
0
a
b
c
d
0
0
0
0
0
0
0
0
15
Index is Valid

• 000000000000000000 0000000001 1100

Tag field
Index field
Offset
Index
0
1
0
a
b
c
d
0
0
0
0
0
0
0
0
16
Index valid, Tag Matches

• 000000000000000000 0000000001 1100

Tag field
Index field
Offset
Index
0
1
0
a
b
c
d
0
0
0
0
0
0
0
0
17
Index Valid, Tag Matches, return d

• 000000000000000000 0000000001 1100

Tag field
Index field
Offset
Index
0
1
0
a
b
c
d
0
0
0
0
0
0
0
0
18
3. Read 0x00000034 000 0..011 0100

• 000000000000000000 0000000011 0100

Tag field
Index field
Offset
Index
0
1
0
a
b
c
d
0
0
0
0
0
0
0
0
19
So read block 3

• 000000000000000000 0000000011 0100

Tag field
Index field
Offset
Index
0
1
0
a
b
c
d
0
0
0
0
0
0
0
0
20
No valid data

• 000000000000000000 0000000011 0100

Tag field
Index field
Offset
Index
0
1
0
a
b
c
d
0
0
0
0
0
0
0
0
21
Load that cache block, return word f

• 000000000000000000 0000000011 0100

Tag field
Index field
Offset
Index
0
1
0
a
b
c
d
0
1
0
e
f
g
h
0
0
0
0
0
0
22
4. Read 0x00008014 010 0..001 0100

• 000000000000000010 0000000001 0100

Tag field
Index field
Offset
Index
0
1
0
a
b
c
d
0
1
0
e
f
g
h
0
0
0
0
0
0
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So read Cache Block 1, Data is Valid

• 000000000000000010 0000000001 0100

Tag field
Index field
Offset
Index
0
1
0
a
b
c
d
0
1
0
e
f
g
h
0
0
0
0
0
0
24
Cache Block 1 Tag does not match (0 ! 2)

• 000000000000000010 0000000001 0100

Tag field
Index field
Offset
Index
0
1
0
a
b
c
d
0
1
0
e
f
g
h
0
0
0
0
0
0
25
Miss, so replace block 1 with new data tag

• 000000000000000010 0000000001 0100

Tag field
Index field
Offset
Index
0
1
2
i
j
k
l
0
1
0
e
f
g
h
0
0
0
0
0
0
26
And return word j

• 000000000000000010 0000000001 0100

Tag field
Index field
Offset
Index
0
1
2
i
j
k
l
0
1
0
e
f
g
h
0
0
0
0
0
0