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System requirements Adobe photoshop CS5 
Windows
» Intel® Pentium® 4 or AMD Athlon® 64 processor
» Microsoft® Windows® XP with Service Pack 3; Windows Vista® Home Premium, Business, Ultimate, or Enterprise with Service Pack 1 (Service Pack 2 recommended); or Windows 7
» 1GB of RAM
» 1GB of available hard-disk space for installation; additional free space required during installation (cannot install on removable flash-based storage devices)
» 1024×768 display (1280×800 recommended) with qualified hardware-accelerated OpenGL graphics card, 16-bit color, and 256MB of VRAM
» Some GPU-accelerated features require graphics support for Shader Model 3.0 and OpenGL 2.0
» DVD-ROM drive
» QuickTime 7.6.2 software required for multimedia features
» Broadband Internet connection required for online services*
Mac OS
» Multicore Intel processor
» Mac OS X v10.5.7 or v10.6
» 1GB of RAM
» 2GB of available hard-disk space for installation; additional free space required during installation (cannot install on a volume that uses a case-sensitive file system or on removable flash-based storage devices)
» 1024×768 display (1280×800 recommended) with qualified hardware-accelerated OpenGL graphics card, 16-bit color, and 256MB of VRAM
» Some GPU-accelerated features require graphics support for Shader Model 3.0 and OpenGL 2.0
» DVD-ROM drive
» QuickTime 7.6.2 software required for multimedia features
» Broadband Internet connection required for online services*
Monggo diikuti langkah2nya buat jadi full :

1. Download dulu Photoshop di situs resmi disini
2. Sebelum install, pastikan sambungan internet anda dimatikan terlebih dahulu
3. Extract File CS5
4. Jalankan Setup
5. Install seperti biasa
6. Setelah selesai klik “Done”
7. Download keygen disini. Buka Keygen CS5 Extended klik “Pacth Host File” , Klik OK
8. Kemudian ketikkan nama anda (bebas), pada Keygen pilih “Adobe Master Collection CS5″
9. Sekarang buka Photoshop. Akan ada permintaan untuk mengisi Serial Number Adobe Photoshop CS5 Extended, Pilihlah opsi “Provide a serial number/SN” selanjutnya Copy dan Paste SN dari Keygen tersebut. Jika sudah memasukkan serial numbernya klik “continue”.
10. Selesai. Photoshop CS5 Extended anda sudah full version.
Update, Cara kedua :
1. Instal Adobe Photoshop CS5 menggunakan lisensi trial
2. Download Adobe CS5 Ultimate Activator Klik Disini 835 kb
3. Cara penggunaannya cukup klik ganda pada CS5 Ultimate Activator lalu klik sembarang tombol pada keyboard anda (2 kali)
4. Selesai
Selamat mencoba gan… Jangan lupa komennya ya
sumber : mastergomaster