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8/8/2019 pertemuan 7 arsiskom
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Wil l iam St a l l ingsCom put er Organizat ion
and Arc h it ec t u re
Chapt er 5
Mem o ri Ex t e rnal
Eppy Yundra, M.T
ep py _yr a@yah oo .c om
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J enis Mem or i Ex t ernal
Magnetic Disk
RAID
Removable
OpticalCD-ROM
CD-Writable (WORM)
CD-R/W
DVD
Magnetic Tape
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Magnet ic Disk
Metal atau plastic dilapisi dg material yg bersifatmagnet (iron oxide)
Jenis kemasan
FloppyWinchester hard disk
Removable hard disk
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Form at dan Organisas i Dat a
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
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Fix ed/Movable Head Disk
Fixed head
Ada satu head (r/w) per track
Head diletakkan pada tangkai yg tetap
Movable headHanya ada satu head per side
Diletakkan pada tangkai yg dpt bergerak
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Rem ovable / Nonrem ovable
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
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Floppy Disk
8”, 5.25”, 3.5”
Kapasitas kecil
sampai 1.44Mbyte (ada yg 2.88M)
LambatUmum dipakai
Murah
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Winc hest er Hard Disk (1)
Dikembangkan oleh IBM di Winchester (USA)
Dikemas dalam satu unit
Berisi satu cakram atau lebih
Head sangat kecil
Handal
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Winc hest er Hard Disk (2)
Umum digunakan
Murah
Sbg external storage yg sangat cepat
Kapasitas semakin besarDalam orde GB
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Rem ovab le Hard DiskZIP
Murah
Banyak digunakan
100MB
JAZMahal
1G
L-120 (a: drive)
Juga dpt untuk membaca 3.5” floppy
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Penc ar ian Sec t or
Harus dapat mengenali awal suatu track dansector
Format disk
Menambahkan informasi tambahanMemberi tanda awal track dan sector
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Gap1 Id Gap2 Data Gap3 Gap1 Id Gap2 Data Gap3
Track SyncByte Head Sector CRC SyncByte
Data CRC
ST506 fo rm at (o ld!)
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Karak te r i s t i k
Fixed head atau movable head
Removable disk atau fixed disk
Single side atau double side
Single platter atau multiple platterMekanisme head
Contact (Floppy)Fixed gap
Flying (Winchester)
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Mul t ip le Pla t t e r
Satu head per side
Semua head di-join dan di-align
Track-track yg setiap platter membentuk
cylinderData dipecah berdasarkan cylinder
Mengurangi gerakan head
Meningkatkan kecepatan (transfer rate)
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RAID
Redundant Array of Independent Disks
Redundant Array of Inexpensive Disks
Ada 6 level
Tidak berhirarkiSejumlah disks (fisik) yg dipandang sbg satu
drive (logical) oleh Sistem Operasi
Data tersebar diantara disk fisik
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RAID 0
No redundancy
Data striped across all disks
Round Robin striping
Increase speedMultiple data requests probably not on same disk
Disks seek in parallel
A set of data is likely to be striped across multipledisks
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RAID 1Mirrored Disks
Data is striped across disks2 copies of each stripe on separate disks
Read from either
Write to both
Recovery is simple
Swap faulty disk & re-mirrorNo down time
Expensive
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RAID 2Disks are synchronized
Very small stripesOften single byte/word
Error correction calculated across corresponding
bits on disksMultiple parity disks store Hamming code error
correction in corresponding positions
Lots of redundancy
Expensive
Not used
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RAID 3
Similar to RAID 2
Only one redundant disk, no matter how largethe array
Simple parity bit for each set of correspondingbits
Data on failed drive can be reconstructed from
surviving data and parity info
Very high transfer rates
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RAID 4
Each disk operates independently
Good for high I/O request rate
Large stripes
Bit by bit parity calculated across stripes oneach disk
Parity stored on parity disk
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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!!!!!
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Opt ic al St orage CD-ROMOriginally for audio
650Mbytes giving over 70 minutes audioPolycarbonate coated with highly reflective coat,
usually aluminum
Data stored as pits
Read by reflecting laser
Constant packing densityConstant linear velocity
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CD-ROM Dr ive 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. 24xThe quoted figure is the maximum the drive can
achieve
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00 00FF
x 10 M i n
S e c
S e c t o r
M o d e
DataLayeredECC
12 byteSync
4 byteId
2048 byte 288 byte
2352 byte
CD-ROM Form at
Mode 0=blank data field
Mode 1=2048 byte data+error correction
Mode 2=2336 byte data
Random Ac c ess on
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Random Ac c ess on
CD-ROM
Difficult
Move head to rough position
Set correct speed
Read address Adjust to required location
(Yawn!)
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CD-ROM for & agains t
Large capacity (?)
Easy to mass produce
Removable
Robust
Expensive for small runsSlow
Read only
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Ot her Opt ic a l St orage
CD-Writable
WORM
Now affordable
Compatible with CD-ROM drives
CD-RW
Erasable
Getting cheaperMostly CD-ROM drive compatible
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DVD - w hat ’s in a nam e?
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 DinnerOfficially - nothing!!!
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DVD - t ec hnology
Multi-layer
Very high capacity (4.7G per layer)
Full length movie on single disk
Using MPEG compressionFinally standardized (honest!)
Movies carry regional coding
Players only play correct region films
Can be “fixed”
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DVD - Wr i t able
Loads of trouble with standards
First generation DVD drives may not read firstgeneration DVD-W disks
First generation DVD drives may not read CD-RW disks
Wait for it to settle down before buying!
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Foreground Read ing
Check out optical disk storage options
Check out Mini Disk
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Magnet ic Tape
Serial access
Slow
Very cheap
Backup and archive
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Digi t a l Audio Tape (DAT)
Uses rotating head (like video)
High capacity on small tape
4Gbyte uncompressed
8Gbyte compressed
Backup of PC/network servers
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Raid
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