William Stallings Computer Organization and Architecture
Chapter 5
Memori External
2
Jenis Memori External
Magnetic Disk
RAID
Removable
Optical
CD-ROM
CD-Writable (WORM)
CD-R/W
DVD
Magnetic Tape
3
Magnetic Disk
Metal atau plastic dilapisi dg material yg bersifat magnet (iron oxide)
Jenis kemasan
Floppy
Winchester hard disk
Removable hard disk
4
Format dan Organisasi Data
Lingkaran konsentris atau track
Ada Gap antar track
Gap sempit, kapasitas bertambah
Jumlah bit per track sama (kerapatan bervariasi)
Kecepatan putar tetap
Track dibagi menjadi beberapa sector
Ukuran minimum block adalah satu sector
Satu block bisa berisi lebih dari satu sector
5
Fixed/Movable Head Disk
Fixed head
Ada satu head (r/w) per track
Head diletakkan pada tangkai yg tetap
Movable head
Hanya ada satu head per side
Diletakkan pada tangkai yg dpt bergerak
6
Removable / Nonremovable
Removable disk
Dapat dilepas dari drive dan diganti dg disk lain
Memberikan kapasitas simpanan yg tak terbatas
Mudah melakukan transfer data antar sistem
Nonremovable disk
Terpasanang permanen dalam drive
7
Floppy Disk
8”, 5.25”, 3.5”
Kapasitas kecil
sampai 1.44Mbyte (ada yg 2.88M)
Lambat
Umum dipakai
Murah
8
Winchester Hard Disk (1)
Dikembangkan oleh IBM di Winchester (USA)
Dikemas dalam satu unit
Berisi satu cakram atau lebih
Head sangat kecil
Handal
9
Winchester Hard Disk (2)
Umum digunakan
Murah
Sbg external storage yg sangat cepat
Kapasitas semakin besar
Dalam orde GB
10
Removable Hard Disk
ZIP
Murah
Banyak digunakan
100MB
JAZ
Mahal
1G
L-120 (a: drive)
Juga dpt untuk membaca 3.5” floppy
11
Pencarian Sector
Harus dapat mengenali awal suatu track dan sector
Format disk
Menambahkan informasi tambahan
Memberi tanda awal track dan sector
12
Gap1
Id
Gap2
Data
Gap3
Gap1
Id
Gap2
Data
Gap3
Track
Sync
Byte
Head
Sector
CRC
Sync
Byte
Data
CRC
ST506 format (old!)
13
Karakteristik
Fixed head atau movable head
Removable disk atau fixed disk
Single side atau double side
Single platter atau multiple platter
Mekanisme head
Contact (Floppy)
Fixed gap
Flying (Winchester)
14
Multiple Platter
Satu head per side
Semua head di-join dan di-align
Track-track yg setiap platter membentuk cylinder
Data dipecah berdasarkan cylinder
Mengurangi gerakan head
Meningkatkan kecepatan (transfer rate)
15
Kecepatan
Seek time
gerakan head ke track yg dituju
(Rotational) latency
Putar platter sampai posisi data dibawah head
Access time = Seek + Latency
Transfer rate
16
RAID
Redundant Array of Independent Disks
Redundant Array of Inexpensive Disks
Ada 6 level
Tidak berhirarki
Sejumlah disks (fisik) yg dipandang sbg satu drive (logical) oleh Sistem Operasi
Data tersebar diantara disk fisik
17
RAID 0
No redundancy
Data striped across all disks
Round Robin striping
Increase speed
Multiple data requests probably not on same disk
Disks seek in parallel
A set of data is likely to be striped across multiple disks
18
RAID 1
Mirrored Disks
Data is striped across disks
2 copies of each stripe on separate disks
Read from either
Write to both
Recovery is simple
Swap faulty disk & re-mirror
No down time
Expensive
19
RAID 2
Disks are synchronized
Very small stripes
Often single byte/word
Error correction calculated across corresponding bits on disks
Multiple parity disks store Hamming code error correction in corresponding positions
Lots of redundancy
Expensive
Not used
20
RAID 3
Similar to RAID 2
Only one redundant disk, no matter how large the array
Simple parity bit for each set of corresponding bits
Data on failed drive can be reconstructed from surviving data and parity info
Very high transfer rates
21
RAID 4
Each disk operates independently
Good for high I/O request rate
Large stripes
Bit by bit parity calculated across stripes on each disk
Parity stored on parity disk
22
RAID 5
Like RAID 4
Parity striped across all disks
Round robin allocation for parity stripe
Avoids RAID 4 bottleneck at parity disk
Commonly used in network servers
N.B. DOES NOT MEAN 5 DISKS!!!!!
23
Optical Storage CD-ROM
Originally for audio
650Mbytes giving over 70 minutes audio
Polycarbonate coated with highly reflective coat, usually aluminum
Data stored as pits
Read by reflecting laser
Constant packing density
Constant linear velocity
24
CD-ROM Drive Speeds
Audio is single speed
Constant linier velocity
1.2 ms-1
Track (spiral) is 5.27km long
Gives 4391 seconds = 73.2 minutes
Other speeds are quoted as multiples
e.g. 24x
The quoted figure is the maximum the drive can achieve
25
00
00
FF
x 10
Min
Sec
Sector
Mode
Data
Layered
ECC
12 byte
Sync
4 byte
Id
2048 byte
288 byte
2352 byte
CD-ROM Format
Mode 0=blank data field
Mode 1=2048 byte data+error correction
Mode 2=2336 byte data
26
Random Access on CD-ROM
Difficult
Move head to rough position
Set correct speed
Read address
Adjust to required location
(Yawn!)
27
CD-ROM for & against
Large capacity (?)
Easy to mass produce
Removable
Robust
Expensive for small runs
Slow
Read only
28
Other Optical Storage
CD-Writable
WORM
Now affordable
Compatible with CD-ROM drives
CD-RW
Erasable
Getting cheaper
Mostly CD-ROM drive compatible
29
DVD -what’s in a name?
Digital Video Disk
Used to indicate a player for movies
⌧
Only plays video disks
Digital Versatile Disk
Used to indicate a computer drive
⌧
Will read computer disks and play video disks
Dogs Veritable Dinner
Officially -nothing!!!
30
DVD -technology
Multi-layer
Very high capacity (4.7G per layer)
Full length movie on single disk
Using MPEG compression
Finally standardized (honest!)
Movies carry regional coding
Players only play correct region films
Can be “fixed”
31
DVD -Writable
Loads of trouble with standards
First generation DVD drives may not read first generation DVD-W disks
First generation DVD drives may not read CD-RW disks
Wait for it to settle down before buying!
32
Foreground Reading
Check out optical disk storage options
Check out Mini Disk
33
Magnetic Tape
Serial access
Slow
Very cheap
Backup and archive
34
Digital Audio Tape (DAT)
Uses rotating head (like video)
High capacity on small tape
4Gbyte uncompressed
8Gbyte compressed
Backup of PC/network servers
